Recently, in order to improve driving safety of a vehicle, there have been proposed technologies that allow a driver to monitor an air pressure, temperature, etc. of a tire detected by a tire condition detection device mounted on a tire side (see patent documents 1, 2 and 3, for example).
An electronic device mounted on a tire side such as a tire condition detection device generally contains a battery as a power source, and an electric load including, for example, sensors such as a pressure sensor and a temperature sensor, and a transmitter that transmits to a vehicle side pressure information, temperature information, etc. from the sensors is driven with the battery.
However, since the power source of the tire-side-mounted electronic device is a single one (power source having consistent discharging characteristics), problems may arise. For example, a chemical battery used for the power source is arranged to produce an electric potential difference between electrodes using a chemical reaction and to supply electric currency to the electric load using the electric potential difference; therefore, the temperature range where the chemical battery can stably act is narrow.
On the other hand, a tire turns into a high temperature state due to heat generated during running, while a tire turns into a low temperature state when a vehicle is parked in a cold region such as a snow district. Accordingly, the battery contained in the tire-side-mounted electronic device may be subjected to a wide-ranging temperature environment from low temperature to high temperature.
Therefore, a chemical battery having a narrow temperature range where it can stably acts may have a case where the electric load can not be driven normally; there is a problem of lacking reliability that electric power is stably supplied from the power source.
Patent Document 1: Japanese patent application Kokai publication No. 2001-250186
Patent Document 2: Japanese patent application Kokai publication No. 2002-331814
Patent Document 3: Japanese patent application Kokai publication No. 2003-182328